This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-110718, filed Apr. 12, 2000; and No. 2000-152828, filed May 24, 2000, the entire contents of both of which are incorporated herein by reference.
The present invention relates to a photo sensor array and a method for manufacturing the same, the photo sensor array being constituted by arranging in two dimensions photoelectric conversion elements (photo sensors) formed of thin film transistors each having a double gate structure provided with a top gate electrode and a bottom gate electrode above and below a common semiconductor layer.
Conventionally, as a two-dimensional image reading device for reading printed matters, photographs, fine uneven configurations along finger prints, there is provided a device of a structure having a photo sensor array which is constituted by the arrangement of the photoelectric conversion elements (photo sensors) in a matrix-like configuration. As such photo sensor arrays, generally a solid imaging device such as a CCD (Charge Coupled Device) or the like is used.
As is known, the CCD has a structure in which photo sensors such as a photo diode, a transistor or the like are arranged in a matrix-like configuration, and an amount (a charge amount) of a pair of an electron and a hole generated in correspondence to a light amount applied to a light receiving portion of each of the photo sensors is detected with a horizontal scanning circuit and a vertical scanning circuit to sense the luminance of the applied light.
In a photo sensor system using such a CCD, since it is required to individually provide a selection transistor for setting each of the scanned photo sensors to a selection state, there is a problem in that the size of the system itself becomes large with an increase in the number of pixels.
Among the photo sensor systems to be applied to the above two-dimension image reading device, pad portions are arranged on the periphery of an array region in which the photo sensors are arranged in a matrix-like configuration. Some of the photo sensors are connected via the pad portions to a peripheral circuit such as a driver or the like for driving the photo sensor array. Here, for example, each of the photo sensors having a TFT structure constituting the photo sensor array has a structure in which a source and a drain electrode, and a gate electrode are provided with respect to a semiconductor layer provided on a glass substrate. Consequently, there is a problem in that since the section structure indispensably has a lamination structure, and the section structures at the array region and the pad portion are made different and individual manufacturing process is applied thereto, the film formation of the conductive layer and the insulating layer and the patterning step remarkably increases so that the manufacturing cost rises and the manufacturing time increases.
Furthermore, in the lamination structure of the photo sensor array, there is a problem in that a difference is generated in the step at the pad portion for connection with the peripheral circuit between the conductive layer formed at a relatively lower layer and the conductive layer formed at a relatively upper layer with the result that a junction with the peripheral circuit is likely to be deteriorated. Furthermore, there is also a problem in that the conductive layer formed on the relatively upper layer becomes more likely to be affected by the step by the conductive layer of the lower layer, and a danger of disconnection becomes high.
An object of the present invention is to provide a photo sensor array and a method for manufacturing the same, the structure being intended to improve a junction between the photo sensor array and a peripheral circuit and suppressing the disconnection of the conductive layer while decreasing the manufacturing process.
A photo sensor array according to a first aspect of the present invention comprises:
a plurality of photo conversion elements separated from each other in a predetermined direction to be arranged, each photo conversion element including a semiconductor layer having an incidence effective region on which excited light is incident, a source and a drain electrode respectively provided on both end sides of the semiconductor layer, a first gate electrode provided below the semiconductor layer via a first gate insulating film, and a second gate electrode provided above the semiconductor layer via a second gate insulating film;
a source terminal commonly connected to the source electrodes of the photo conversion elements;
a drain terminal commonly connected to the drain electrodes of the photo conversion elements;
a first gate terminal commonly connected to the first gate electrodes of the photo conversion elements; and
a second gate terminal commonly connected to the second gate electrodes of the photo conversion elements,
at least one of the first gate electrode and the second gate electrode provided on the photo conversion elements being constituted of a first transparent electrode layer, and at least one of the source terminal, the drain terminal, and the gate terminal being constituted with the first transparent electrode layer.
According to the first aspect of the present invention, any of the source terminal, the drain terminal, the first gate terminal and the second gate terminal has a lamination structure including the transparent electrode layer which constitutes the first gate electrode or the second gate electrode. Thus, a favorable electric connection state with the peripheral circuit can be realized while lowering a sheet resistance which allows a thick formation of the structure of each terminal, and suppressing the failure in the configuration of the terminal. In particular, when the transparent electrode layer is made of ITO, a junction with the peripheral circuit can be improved as compared with the metal terminal other than the ITO.
The uppermost layer of at least any one of the source terminal, the drain terminal, and the first gate terminal may be constituted of the first transparent electrode layer. As a consequence, each of the terminals may be formed in a lamination layer by using the same material and the same process as the electrode layer formed on the incident side of the excited light with respect to the semiconductor layer.
Here, the photo sensor array comprises an electrostatic electricity discharging and contact sensing electrode provided via an insulating film above the photoelectric conversion terminals. When at least any one of the source terminal, the drain terminal, the first gate terminal and the second gate terminal is constituted with the second transparent electrode layer which constitutes the electrostatic electricity discharging and contact sensing electrode, it is possible to prevent the electrostatic breakdown and operation failure of the circuit such as a driver or the like with the contact of fingers on which static electricity is electrified. Thus, the driving of the photo sensor array can be automatically started.
Furthermore, at least as a lower layer of the source and the drain electrodes, the source and the drain terminals and the source-drain wiring, a semiconductor layer may be extended and provided. As a consequence, the lamination structure of each terminal portion can be made thick, and the configuration failure of the terminal is further suppressed, and a junction with the peripheral circuit can be further improved. Additionally, a step generated on the conductive layer such as an insulating layer provided on the layer upper than the semiconductor layer, the second gate electrode or the like can be alleviated, so that the deterioration of the insulating properties and the signal transmission properties can be suppressed.
Furthermore, the plurality of photoelectric conversion elements having the above structure are connected via terminals to a predetermined peripheral circuit such as a drain driver, a first gate driver, a second gate driver or the like, so that the photo sensor system having a favorable insulating properties, signal transmission properties, and junction can be manufactured in a simple manufacturing process.
Furthermore, the effective region on which excited light between the source-drain electrodes of the semiconductor layer is incident can be constituted so as to easily satisfy the predetermined configuration ratio, thus, the incidence effective region can be arbitrarily arranged to improve the deviation of the light sensing region. Consequently, since the incidence effective region of the semiconductor layer can be set so that the optimal configuration ratio can be provided, a sufficient source-drain current is allowed to flow even when the incident light of the excited light is very small. Thus, a favorable light receiving sensitivity can be realized.
With such a photo sensor array, the source electrodes of the semiconductor layers are connected to each other, the drain electrodes of the semiconductor layers are connected to each other, the source electrodes or the drain electrodes may be formed over two adjacent semiconductor layers out of the semiconductor layers.
Besides, the semiconductor layers of the photo conversion elements may be arranged along the directions of the channel length of the semiconductor layers.
Furthermore, when the photoelectric conversion elements are arranged in a delta configuration, the distance between the photoelectric conversion elements adjacent to each other in two dimensions can be made more even. Consequently, it is possible to suppress the deviation in the light information resulting from the unevenness in the light receiving sensitivity which differs in accordance with the direction at the time when the same subject to be photographed is placed at a planarly different angle with respect to the photo sensor array. Limitation on the angle at which the subject is placed can be small so that a photo sensor array excellent in the image reading properties can be realized.
A method for manufacturing a photo sensor array according to a second aspect of the present invention comprises:
forming a first gate electrode on an insulating film and a first gate base pad connected to the first gate electrode on a first gate terminal portion;
forming a first gate insulating film on at least the first gate electrode and the first gate terminal portion, then forming a semiconductor layer having a predetermined configuration above the first gate electrode for generating a carrier with excited light;
forming a first open portion for exposing the first gate base pad to the first gate terminal portion;
forming source and drain electrodes respectively provided on both ends of the semiconductor layer, a drain base pad connected to the drain electrode on the drain terminal portion, and a first gate terminal lower layer on the first gate terminal portion via the first open portion;
forming a second insulating film on at least the first gate terminal lower layer, the source-drain electrode, and the drain terminal portion, then forming a second open portion for exposing at least one of the first gate terminal lower layer and the first drain base pad; and
forming a second gate base pad connected with the second gate electrode on the second gate electrode having a predetermined configuration and the second gate terminal portion above the semiconductor layer while forming via the second open portion at least one of the first gate terminal upper layer connected to the first gate terminal lower layer and a drain terminal upper layer connected to the drain base pad.
According to this manufacturing method, since the electrode layers which constitute any one of the first gate terminal and the drain terminal are laminated and formed with the same material and the same steps as the conductive layers of the photo conversion elements constituting a photo sensor array, each structure of the whole photo sensor array can be constituted and processed in a common series of manufacturing process. Thus an attempt can be made to decrease the manufacturing processes and reduce the manufacturing cost and manufacturing time. At the same time, the electrode layers which constitute any of the first gate terminal and the drain terminal can be favorably made thick and the sheet resistance of the terminal can be lowered.
In addition, on the protection insulating film, the electrostatic electricity discharging and contact sensing electrode, the first gate terminal uppermost layer or the drain terminal uppermost layer or the second gate terminal upper layer may be formed in the same process. This enables to prevent the electrostatic breakdown and operation failure of the photoelectric conversion elements by the charge electrified on the subject without increasing the manufacturing process. In addition, the junction with the peripheral circuit can be further improved by making the lamination structure of each terminal thick.
Furthermore, out of the lamination structure constituting the drain terminal, the first gate terminal and the second gate terminal, at least the conductive layer constituting the uppermost layer may be constituted of a transparent electrode layer. This enables to form the lamination of each terminal without increasing the manufacturing process by using the same material and the same process with the electrode layer formed on the incident side of excited light with respect to the semiconductor layer.
Furthermore, the semiconductor layer may be extended and provided on a lower layer of the source-drain electrode, the source-drain terminal and the source-drain wiring. Thus, the lamination structure of each terminal portion is made thicker, the sheet resistance is lowered, and configuration failure of the terminal is suppressed, and junction with the peripheral circuit can be further improved. In addition a step generated on the insulating layer provided on the upper layer than the semiconductor layer or on the conductive layer such as the second gate electrode or the like is alleviated so that the photo sensor system which can suppress the deterioration in the insulation properties and signal transmission properties can be provided in a simple manufacturing process.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.